1. Field of the Invention
The present invention relates to a recovery method in a case of failure on a route for transmitting a control signal in a radio communication system, and to a radio network controller comprising such a recovery function.
2. Description of the Related Art
Radio communication systems such as a mobile communication system comprise a plurality of base transceiver stations (BTS) (also referred to as node B), and mobile stations (MS) (also referred to as user equipment (UE)) such as cellular phone devices are accommodated by the nearest base transceiver station. A radio network controller (RNC) is connected to a single or a plurality of base transceiver station(s). The radio network controller controls the base transceiver station(s), and also controls mobile stations accommodated by the base transceiver station.
FIG. 1 is a diagram showing a configuration of a radio network controller. In the diagram, a configuration specified by 3GPP is shown as an example.
A radio network controller 10 comprises a plurality of MS control signalling devices 11, a BTS control signalling device 12, and a selection/combination device 13. The MS control signalling device 11 terminates DCCH (Dedicated Control Channel), and executes processing relating to RLC (Radio Link Control) protocol specified by 3GPP.TS25.322. The MS control signalling devices 11 also transmits/receives a control signal (e.g. instructions such as call request and call ending) to/from a mobile station 30. The BTS control signalling device 12 terminates CCCH (Common Control Channel), and transmits/receives a control signal to/from a base transceiver station 20. The selection/combination device 13 relays a signal between the base transceiver station 20 and a correspondent node (CN) 40. Here, the selection/combination device 13 comprises a selecting/combining function, a copy/distributing function, and a cipher/decipher function. The selecting/combining function is for selecting a signal having the best quality when a signal transmitted from the mobile station 30 is received via a plurality of base transceiver stations 20. The copy/distributing function is for transmitting a signal directed to the mobile station 30 via the plurality of base transceiver stations 20. The cipher/decipher function is for ciphering and transmitting a user signal as well as deciphering the received ciphered signal to regenerate the user signal. An application 14 and a platform (PF) 15 are software executed by a call control processor, and provide communication services by controlling the MS control signalling devices 11, the BTS control signalling device 12, and the selection/combination device 13.
An MS control signal for controlling communication relating to the mobile station 30 is transmitted/received between the application 14 and the mobile station 30. Here, between the application 14 and the MS control signalling device 11, an MS control signal 1 of RRC (Radio Resource Control) layer is transmitted/received. Between the MS control signalling device 11 and the mobile station 30, an MS control signal 2 of an RLC layer is transmitted/received. On the other hand, a common control signal 3 for controlling the base transceiver station 20 is transmitted/received between the application 14 and the base transceiver station 20. User data 4 is, in the example shown in FIG. 1, transmitted/received via the selection/combination device 13. In such a case, the MS control signal 2 is also transmitted/received via the selection/combination device 13.
FIG. 2 through FIG. 5 are diagrams explaining recovery procedures in a case that the MS control signalling device 11 fails in the radio network controller 10. In this diagram, the radio network controller 10 comprises a plurality of MS control signalling devices 11 (11-1, 11-2, . . . ), and the MS control signalling device 11-1 is assigned to the mobile station 30.
When the MS control signalling device 11-1 fails, as shown in FIG. 2, the MS control signals 1 and 2 that are transmitted/received by the MS control signalling device 11-1 stop. The application 14 then releases a data path of the mobile station 30 controlled by the MS control signalling device 11-1 as shown in FIG. 3. As a result, the mobile station 30 cannot receive the MS control signal 2 and the user data 4, and detects the network failure accordingly.
The mobile station 30, when detecting the failure, transmits a reconnection request using the common control signal 3 as shown in FIG. 4. This reconnection request is received by the application 14. The application 14 sends back a reconnection response to the mobile station 30 via another MS control signalling device (in this case, the MS control signalling device 11-2). Since then, the mobile station 30 transmits/receives the MS control signal 2 to/from the MS control signalling device 11-2.
In addition, the application 14, as shown in FIG. 5, acquires the data path for transmitting the user data 4 of the mobile station 30, and notifies the selection/combination device 13 of the data path. As a result, the data path for transmitting the user data 4 of the mobile station 30 recovers.
Note that Patent Document 1 (Kohyo (National Publication of Translated Version) No. 2005-510155) describes a method in a mobile communication system comprising a radio network controller, a radio transceiver station, and a mobile station to acquire environment information from a mobile station when the radio network controller recovers from failure. In this document, the environment information identifies each mobile station. The radio network controller recovers communication of the mobile station using the environment information.
As explained above, in the conventional technologies, when an MS control signalling device fails, a data path for transmitting user data is once released. For that reason, when the MS control signalling device fails during a mobile station is transmitting/receiving audio data, there occurs a several seconds of silence. The above recovery procedures are executed upon the reconnection request from the mobile station. In other words, the radio network controller could not execute the recovery procedure autonomously.
Note that the above problem can occur not only in the case of an MS control signalling device failure but also in a case that a failure occurs on a route for transmitting an MS control signal and in a case that the service is suspended due to blockage etc.